Turbulence characteristics in rough non-uniform open-channel flow

Laboratory experiments on the turbulence structure of rough, non-uniform open-channel flow are reported, Velocity, turbulence-intensity and Reynolds-stress profiles were measured, It was found that: (a) non-uniform flow can be parameterized by using an equilibrium pressure-gradient parameter defined as beta = (D/tau(0))(partial derivative p*/partial derivative x); beta = -1 for uniform, beta < -1 for accelerating, and B > -1 for decelerating flow; (b) the universal law of the wall explains the inner-region data; in the outer region, the data follow the Coles' law of the wake, whose Pi-values depend on the pressure-gradient parameter beta; (c) the turbulence intensities u'/u* and v'/u*, as well as the Reynolds stress -<(u(f)v(f))over bar>/u(2)* decrease in accelerating and increase in decelerating flows (compared with the ones in uniform flow); (d) the eddy viscosity v(t)/delta u* decreases in accelerating and increases in decelerating flow; (e) the energy spectra for non-uniform flow are essentially the same as for uniform flow and display the inertial sub-range characteristics.